Backlight-type liquid-crystal displays, liquid-crystal TVs, illumination signboards and others with a built-in light source therein have been much popularized. Of such backlight-type built-in light sources (planar light sources), a typical structure of an underlight-type backlight comprises, as in FIG. 2, a housing 11 that serves both as a profile case and as a light reflector, a diffuser 14, and a light source such as a cold-cathode lamp 15. A typical structure of a sidelight-type backlight comprises, as in FIG. 3, a light waveguide with a dot print 12 on a transparent acrylic plate 13, a light reflector 11, a diffuser 14, and a light source such as a cold-cathode lamp 15. In these, the light from the light source is reflected on the light reflector, and forms uniform planar light though the diffuser. With the recent tendency toward large-size displays, some improvements have been made also in light sources for illumination devices by increasing their output power and by increasing the number of the light source lamps therein. For increasing the brightness of these devices, plural light sources may be disposed, as in FIG. 2 and FIG. 3.
Heretofore for the light reflectors for such applications, the housing for the profile case is often painted white or a white polyester film (e.g., Patent Reference 1) is much used. However, the white painting could not satisfactorily increase the brightness by reflected light, and a light reflector that comprises a white polyester film is often problematic in point of its discoloration (yellowing) owing to the recent increase in the quantity of light, and materials that are less discolored have become desired. Accordingly, a light reflector that comprises a white polyolefin film is proposed (e.g., Patent References 2 to 5).
Patent Reference 1: JP-A 4-239540
Patent Reference 2: JP-A 6-298957
Patent Reference 3: JP-A 2002-31704
Patent Reference 4: JP-A 8-262208
Patent Reference 5: JP-A 2003-176367